1. Field of the Invention
The present invention relates to transforming growth factor beta (TGF-beta or TGFβ) antagonists and method for treating or ameliorating symptoms of cancer and other human diseases including therapeutically active portions of at least two soluble TGF isoform receptors.
More particularly, the present invention relates to TGF-beta antagonists and method for treating or ameliorating symptoms of cancer and other human diseases, where the TGF-beta antagonists include a mixture or combination of therapeutically active portions of sRII and therapeutically active portions of sRIII and/or to a fusion protein including therapeutic portions of sRII and/or sRIII and the method includes administering to an animal including a human a therapeutically active amount of the combination.
2. Description of the Related Art
TGFβ, its Signal Transduction and its Function. Transforming growth factor beta (TGFβ) isoforms, named β1, β2, and β3 from mammals, are homodimeric polypeptides of 25 kDa. They are secreted in a latent form and only a small percentage of total secreted TGFβs is activated under physiological conditions. TGFβ binds to three different cell surface receptors called type I (RI), type II (RII) and type III (RIII) receptors. RIII (also called betaglycan) has two TGFβ binding sites in its extracellular domain, which are called the E and U domains. It can sequester and present the ligand to RII to augment TGFβ activity when it is membrane-bound (Chen et al., 1997; Lopez-Casillas et al., 1993; Wang et al., 1991; Fukushima et al., 1993; Lopez-Casillas et al., 1994). TGFβ1 and TGFβ3 can bind RII with high affinity; however, TGFβ2 requires RIII for binding to RII. RI and RII are serine/threonine kinase receptors. Binding of TGFβ to RII recruits and activates RI through phosphorylation (Wrana et al., 1994). The activated RI phosphorylates intracellular Smad2 and Smad3, which then interact with Smad4 protein to regulate gene expression in the nucleus (Piek et al., 1999; Massague and Chen, 2000). Through its regulation of gene expression, TGFβ has been shown to influence many cellular functions such as cell proliferation, differentiation, cell-cell and cell-matrix adhesion, cell motility, and activation of lymphocytes (Massague, 1990; Roberts and Spom, 1991). TGFβ has also been shown or implicated to induce or mediate the progression of many diseases such as osteoporosis, hypertension, atherosclerosis, hepatic cirrhosis and fibrotic diseases of the kidney, liver and lung (Blobe et al., 2000). Perhaps, the most extensively studied function of TGFβ is its role in tumor progression as summarized below.
Loss of TGFβ's Growth Inhibitory Activity During Tumor Progression. TGFβs have been shown to be potent growth inhibitors in various cell types including epithelial cells (Lyons and Moses, 1990). The mechanism of the growth inhibition by TGFβ is mainly due to the regulation of cell cycle-related proteins (Derynck, 1994; Miyazono et al., 1994). Thus, aberrant regulation of cell cycle machinery such as loss of retinoblastoma gene product during tumorigenesis can lead to loss of growth inhibition by TGFβ. Furthermore, mutational inactivation of TGFβ receptors, Smad2 and Smad4 has been reported in various carcinomas (Massague et al., 2000). For example, loss of RI and/or RII expression is often observed in some human gastrointestinal cancers (Markowitz and Roberts, 1996).
TGFβ's Tumor-promoting Activity. While many carcinoma cells lose response to TGFβ's growth inhibition, they often overproduce active TGFβ isoforms when compared to their normal counterpart (Reiss, 1999). This is likely to result in the selection of cancer cells that are resistant to TGFβ's growth inhibitory activity. Indeed, an increased level of TGFβ1 is strongly associated with the progression of many types of malignancies and poor clinical outcome (Reiss, 1999). For example, serum TGFβ1 levels have been shown to correlate to tumor burden, metastasis, and serum prostate specific antigen (PSA) in prostate cancer patients (Adler et al., 1999; Shariat et al., 2001). Consistent with these observations, marked increase of TGFβ1 and TGFβ2 expression was observed in an aggressive androgen-independent human prostate cancer cell line when compared to its less aggressive androgen-dependent parent cell line, LNCap (Patel et al., 2000).
Several mechanisms are believed to mediate TGFβ's tumor-promoting activity (Arteaga et al., 1996; Reiss, 1999). TGFβ is a potent immune suppressor (Sosroseno and Herminajeng, 1995). Overexpression of TGFβ1 in the rat prostate cancer cells was associated with a reduced immune response during tumor formation suggesting that TGFβ may suppress host immune response to the growing tumor (Lee et al., 1999). TGFβ has also been shown to be angiogenic in vivo (Fajardo et al., 1996; Yang and Moses, 1990; Wang et al., 1999). Overexpression of TGFβ during cancer progression is often associated with increased angiogenesis and metastasis suggesting that TGFβ may promote metastasis by stimulating tumor blood vessel formation (Roberts and Wakefield, 2003). TGFβ also plays an important role in promoting bone metastasis of human prostate and breast cancers (Koeneman et al., 1999; Yin et al., 1999). Both TGFβ1 and TGFβ2 are produced by bone tissue, which is the largest source of TGFβ in the body (Bonewald and Mundy, 1990). The latent TGFβ can be activated by proteases such as PSA and urokinase plasminogen activator, which are abundantly secreted by cancer cells (Koeneman et al., 1999). Taken together, TGFβ can act in tumor microenvironment to promote carcinoma growth, angiogenesis and metastasis.
Development of TGFβ Antagonists. Because of its involvement in the progression of various diseases, TGFβ has been targeted for the development of novel therapeutic strategies. One way of antagonizing TGFβ activity is to utilize the ecto-domain of TGFβ type II receptor or type III receptor, also known as betaglycan (BG). We have previously shown that ectopic expression of a soluble BG (sBG, also called sRIII) containing the whole ecto-domain of BG in human carcinoma cell lines can significantly inhibit tumor growth, angiogenesis, and metastasis when they are inoculated in athymic nude mice (Bandyopadhyay et al., 1999; Bandyopadhyay et al., 2002b). More recently, we have shown that systemic administration of a recombinant sBG can also inhibit the growth, angiogenesis and metastasis of the xenografts of human breast carcinoma MDA-MB-231 cells in nude mice (Bandyopadhyay et al., 2002a). However, the inhibition was only partial, not complete. This could be due in part to the fact that both active TGFβ1 and TGFβ2 were produced by the cells and the anti-TGFβ potency of sBG is 10-fold lower for TGFβ1 than for TGFβ2 (Vilchis-Landeros et al., 2001). Interestingly, while the extracellular domain of RII (sRII) has very low affinity for TGFβ2, its affinity for TGFβ1 and TGFβ3 is more than ten times higher than that of sBG (Lin et al., 1995; Vilchis-Landeros et al., 2001).
While numerous TGF antagonists have been prepared and tested, all have less than complete TGF isoform inhibiting properties. Thus, there is a need in the art for a class of generalized TGF antagonists or inhibitors which can inhibit all three isoforms of TGF, simultaneously.